If targeted programs can be poorly designed or mismanaged inconsistently, then so could UBI. The whole idea is to thoughtfully design a program. If that is possible, there's no reason we can't thoughtfully design targeted programs, and UBI would still be there in a lesser capacity precisely for those people that would fall through the cracks of those targeted programs.
UBI just feels like a kind of sledgehammer, when a dozen scalpels might perform better. I'll grant that UBI would be superior to the very loose "safety net" of social programs in the US though.
Even with a "strong" UBI program, I still think we'd need other programs as well-- UBI will be far too low for people that suddenly lose a job that pays 5x UBI and need to get by until they find new comparable employment, as an example.